An autogyro aircraft is piloted by a person and derives lift from an unpowered, freely rotating rotary wing or plurality of rotary blades. The energy to rotate the rotary wing results from the forward movement of the aircraft in response to a thrusting engine such as an onboard motor that drives a propeller. During the developing years of aviation aircraft, autogyro aircraft were proposed to avoid the problem of aircraft stalling in flight and to reduce the need for runways. The relative airspeed of the rotating wing is independent of the forward airspeed of the autogyro, allowing slow ground speed for takeoff and landing, and safety in slow-speed flight. Engines are controlled by the pilot and may be tractor-mounted on the front of the pilot or pusher-mounted behind the pilot on the rear of the autogyro. Airflow passing the rotary wing, which is tilted upwardly toward the front of the autogyro, provides the driving force to rotate the wing. The Bernoulli Effect of the airflow moving over the rotary wing surface creates lift.
U.S. Pat. No. 1,590,497 issued to Juan de la Cierva of Madrid, Spain, illustrated a very early embodiment of a manned autogyro. Subsequently, de la Cierva obtained U.S. Pat. No. 1,947,901 which recognized the influence of the angle of attack of the blade of a rotary wing. The optimum angle of attack for the blades or rotary wing was described by Pitcairn in U.S. Pat. No. 1,977,834 at about the same time. In U.S. Pat. No. 2,352,342, Pitcairn disclosed an autogyro with blades which were hinged relative to the hub.
Even though the principal focus for low speed flight appears to have shifted to helicopters, there appears to have been some continuing interest in autogyro craft. However, development efforts appear to have largely been restricted to refinements of the early patented systems. For instance, Salisbury, et al., U.S. Pat. No. 1,838,327, showed a system to change the lift to drag response of a rotary wing.
The value of being able to elevate a sensor for surveillance is recognized in the art. Flight vehicles offer the opportunity to elevate a sensor to great advantage, the earliest military examples of this being the use of tethered balloons.
Tethered balloons and aerostats remain in use today for surveillance, but can require significant resources to transport, set-up, maintain, and tear down, limiting their utility to specific applications. Great reliance has instead been placed on the use of piloted surveillance aircraft (such as airplanes and helicopters. While aircraft operations offer tremendous mobility and flexibility, they also come at significant expense, significant facility and logistical burdens, and with limited flight endurance.